This study was performed to investigate the effect of co-existence of carbaryl and chlorothalonil on the short-term bioconcentration factor in Carassius auratus(goldfish). The fishes were exposed to the combined treatment of carbaryl and chlorothalonil(0.05 ppm+0.005 ppm, 0.05 ppm+0.010 ppm, 0.10 ppm+0.005 ppm) for 1, 3 and 5 days, respectively. Carbaryl and chlorothalonil in fish and in test water were extracted with n-hexane and acetonitrile. GC-ECD was used to detect and quantitate carbaryl and chlorothalonil. 1-day, 3-day and 5-day bioconcentration factors($BCF_1, BCF_3$ and $BCF_5$) of each pesticide were calculated from the quantitation results. The depuration rate of each pesticide from the whole body of fish was determined over the 72-h period after combined treatment. The results were as follows: $BCF_1$ values of carbaryl were 3.521, 3.802 and 3.587, respectively, when the concentration of carbaryl and chlorothalonil in combined treatment were 0.05+0.005, 0.05+0.010 and 0.10+0.005 ppm. BCF3 values of carbaryl were 4.825, 4.556 and 3.828, respectively, and $BCF_5$ values of carbaryl were 3.974, 3.921 and 4.186, respectively, under the conditions. While $BCF_1$ of chlorothalonil were 0.829, 0.829 and 1.540, respectively, under the same condition of pesticide concentrations $BCF_3$ of chlorothalonil were 2.040, 2.208 and 3.633, respectively, and $BCF_5$ of chlorothalonil were 6.222, 6.667 and 7.095, respectively, under the conditions. Depuration rate constants of carbaryl were 0.022, 0.022 and 0.152, respectively, when the concentration of carbaryl and chlorothalonil in combined treatment were 0.05+0.005, 0.05+0.010 and 0.10+0.005 ppm. While depuration rate constants of chlorothalonil were 0.004, 0.004 and 0.006, respectively, under the same condition of pesticide concentrations. It was observed that no significant differences of carbaryl and chlorothalonil concentration in fish extracts, test water and $BCF_s$ of carbaryl and chlorothalonil between combined treatment and single treatment. It was considered that no appreciable interaction at experimental concentrations was due to low concentrations, 0.005~0.1 ppm. Co-existence of carbaryl and chlorothalonil had no effect on excretion of each pesticide and depuration rate of chlorothalonil was investigated 1/8 slower than that of carbaryl in combined treatment. Therefore, it is considered that the persistence of chlorothalonil in fish body would be higher than that of carbaryl.